The present invention is directed to a method for blow molding a hollow article having an integral projection extending from a wall thereof, such as, a bottle with an integral handle.
There is a continuous demand, particularly in the food and beverage industry, for articles, such as bottles, buckets, pitchers, etc., made of clear, tough plastic because they are relatively inexpensive, easy to use, generally non-breakable and serve as good substitutes for glass. It is oftentimes desirable that such articles have handles to aid in their use, particularly large bottles.
However, it is generally understood that PET lacks sufficient hot melt strength to be extrusion blow molded and it work hardens thereby preventing it from entering shallow areas or forming sharp corners of a mold which form an integral handle. As a result, integrally molded handles on PET bottles have been susceptible to breakage, especially when molded in bottles of larger sizes. The bottle industry has sought an integral-handled PET bottle since PET was first commercially available in 1977. Eastman, DuPont, and other PET resin manufacturers developed a modified PET, called E-PET, that allowed the composition to be extrusion blow molded to form bottles with handles for detergents, milk, etc. However, these bottles were not properly oriented and shattered when drop tested. Also, E-PET was costly and efficiencies in production could not be utilized to reduce the bottles"" cost.
Thus, when PET was used and handles were desired, it had been the practice to attach the handle to the PET article in a separate operation, such as by ultrasonic fusion, after the blow molded PET article had been formed in, and removed from, the blow mold. U.S. Pat. No. 4,727,997 discloses a method and apparatus for producing a PET bottle with a PET handle. In a first step, a parison is blow molded in a blow mold which has inwardly extending circumferential ridges to produce a blown bottle with article-encircling grooves therein. In a second step, the blow molded bottle is transferred to a second grip forming mold, which has circumferential grooves therein, and a handle is injection molded onto the bottle.
Another approach has been to injection mold a thermoplastic handle in an separate operation from the blow molding of the container, and then to snap the separately molded handle over the neck or finish of the blown PET bottle. In accordance with a still further proposal, the separately molded handle is inserted into the blow mold and the bottle is blown over, or into, the handle.
The inventor of the present invention. Samuel L. Belcher, has also previously attempted to overcome the problems associated with forming PET bottles with durable integral handles. U.S. Pat. Nos. 4,992,230, 4,993,931 and 5,057,266 all disclose a method and apparatus for making a hollow blow molded PET article with an integral external projection such as a handle. The method includes blow molding the hollow article and then injection molding the integral projection thereon. The apparatus includes a combination mold having separate and independent blow mold and injection mold cavities which communicate at an interface therebetween. In essence, in the method and apparatus of that invention, a PET preform is inserted into a combination blow mold and injection mold wherein the blow mold cavity defines article (bottle) to be blown and the injection mold cavity defines the handle. The blow mold and injection mold cavities are in communication with each other at a location defining the area where the handle is to extend from the container. After insertion into the blow mold, the preform is injected with blow gas from a gas nozzle to conform the preform to the blow mold cavity thereby forming the hollow blow molded bottle. While the pressure of the blow gas holds the preform in conformity with the blow mold cavity, and prior to exhausting the blow gas, molten PET is injected under pressure into the injection mold cavity to form the integral handle and bond it to the blown preform bottle at the point where the injection mold cavity communicates with the blow mold cavity. The combination mold is then opened and the finished bottle is removed.
It is also known to form chimes in drums and handles in bottles by trapping materials in extruded plastic parisons where there is significant waste of polymeric materials.
None of the above practices, however, has been entirely satisfactory in making PET bottles with integral handles since they add steps to the fabrication process, utilize extra materials, and employ complicated molds. Furthermore, other known methods requiring ultrasonic bonding equipment or multiple separate molds are unduly time-consuming, unnecessarily expensive and still do not overcome the handle breakage problem seen in larger bottles or containers.
The present invention overcomes the above problems by providing a new method of forming an integral handle or projection on a hollow plastic article such as a bottle. The method involves first blow molding a thermoplastic, preferably PET, into the shape of a bottle and thereafter pinching the side wall of the blown bottle so as to bond adjacent interior wall surfaces together and integrally form the handle. This method thus avoids material waste associated with prior practices.
In the preferred method of this invention, a PET preform is inserted into the blow mold cavity which defines a bottle shape. In the blow mold, each cavity half has a handle contour shape and a movable mold segment which cooperates with another segment to define the integral handle or projection extending from the blown bottle. The movable mold segments are in a first retracted position which creates a void around each segment since the recessed metal segment occupies one-half of the handle to body radius that blends the handle to the body. After inserting the PET preform into the bottle-defining blow mold cavity, a stretch rod is inserted into the interior of the preform to stretch the preform a predetermined amount. The PET preform is then injected with a first blow gas to conform the preform to the blow mold cavity, thereby forming the hollow blow molded bottle. PET, with its unique strain hardening, when being expanded under heated conditions from the preform shape, will not blow into the segment voids in the closed blow mold. Rather, the PET of the preform will slide over these voids and fill the mold cavity. Thus, the method takes advantage of this material characteristic of PET when blowing the heated preform into the blow mold cavity with the movable handle segments retracted. These phenomena also allow for the PET to stretch under pressure of the moving segment into the handle-forming position and take the desired bottle shape with a handle.
Prior to blowing the preform in the blow mold cavity, the preform temperature is established at the desired level. For example, if PET is used, the preform temperature is established at its stretch temperature, which is well know for PET to be in the range of about 190xc2x0 F. to about 265xc2x0 F. The preform may be one previously made on another machine which is heated to the stretch temperature range in a separate heating operation prior to insertion into the blow mold, or it may be a previously injection molded PET preform (as on a single-stage PET machine) that has cooled to the appropriate stretch temperature immediately prior to insertion in the blow mold cavity.
Substantially immediately subsequent to blow molding, while the pressure of the first blow gas holds the preform in conformity with the blow mold cavity, and prior to exhausting the blow gas and opening the blow mold, a second blow gas is discharged from a hole in the stretch rod so as to impinge an interior wall of the bottle where the handle is to be formed. With the second blow gas impinging the interior wall of the bottle, the movable mold segments are advanced within the blow mold cavity from a first retracted position to a second position thereby compressing one surface of the interior wall into contact with an opposing surface of the interior wall to form therebetween an integral handle extending away from the exterior wall of the blow molded bottle. The integral protrusion or handle, is formed in the area of the blown preform bottle at the interface where the movable mold segments communicate within the blow mold cavity. After the handle is formed, the mold segments are retracted and the blow mold is opened. The finished bottle is removed and may be trimmed of excess material. The material in the bonded area of the bottle may be trimmed to form a handle opening in the bottle with a reinforcing rib along the interior of the opening.
According to the method of this invention, the handle and bottle are from the same PET parison. Thus, the handle is integral and properly oriented to the hollow blown bottle. Accordingly, there is no need for separate steps of injection molding, ultrasonic bonding, adhesive bonding, snap-on fittings, container encircling rings, or the like. Rather, these steps and materials are avoided by the method of this invention.
Other advantages of the method include utilizing standard PET resins and preforms, and standard PET bottle blow molding machines including wheel, in-line and single stage machines. Most importantly, finished thermoplastic or PET bottles with integral handles as made by the present invention, especially larger bottles, are biaxially-oriented to pass drop tests with filled product. The handles withstand the stresses and weight requirements of containers, especially larger bottles of greater than 32 ounces. Due to the biaxial orientation, the bottles also have increased barrier properties and hot fill capabilities, and satisfy all bottle markets including food, beverage, personal care, medical, liquor, packaging and the like.
In accordance with the novel features and embodiments of this invention which will become further apparent hereinafter, the present invention will be described with reference to the detailed description and the accompanying drawings in which: